A general description of well technology is discussed in U.S. Pat. No. 6,372,678, entitled “Proppant Compositions for Gas and Oil Well Fracturing,” which issued Apr. 16, 2002 and is hereby incorporated by reference.
In the drilling, completion and operation of oil wells, gas wells, water wells and similar boreholes, it frequently is desirable to alter the producing characteristics of the formation by treating the well. Many such treatments involve the use of particulate material. For example, in hydraulic fracturing, particles called proppants are used to maintain the fracture in a propped, or open, condition. Common proppants used in the well industry are composed of sand, resin coated sand, ceramics, walnut shells, sintered bauxite, clay, engineered particulates and other solid particles.
The rock formations and liquids associated with oil and gas production are known to contain dissolved and suspended ions, compounds and solids that can be hazardous to human health and the environment. Conditions in the rock formation including rock composition, rock solubility, pressure and interstitial and formation water content can cause undesirable chemical elements and compounds to form in underground water and in waters injected into a rock formation. Examples of chemical elements and compounds that develop and concentrate in oilfield waters are heavy metals, organometallics, inorganic salts and organic compounds. When the hydrofacturing waters flow back to the surface or are produced at the surface, the presence of metals and other inorganic and organic compounds limit reuse of the water and represent a disposal and handling hazard to humans, wildlife and the environment.
Hydrofracturing commonly utilizes three to ten million gallons of water per single well application. While a high percentage of the water remains down hole, a significant number of gallons return up the well bore to the surface as flow back water and eventually as produced water at the well site. Reuse of this water is desirable for continued fracturing fluid make-up and other production associated uses especially in drought restricted areas. The presence of water soluble metals and other contaminants from down hole often limit this reuse and typically require wastewater treatment at the surface. In addition, when the disposal of flow back water and produced water is necessary it is restricted by the presence of metals, organometallics, inorganic salt and organic soluble contaminants.
All metals, including heavy metals and D-block metals, can be present in the waste liquids. Especially hazardous are mercury, selenium, arsenic, antimony and cadmium. In addition other constituents such as cyanide, fluoride and boron can contaminate flow back and produced waters. Typical inorganic salt contaminants are sodium, magnesium and calcium chlorides, sulfates, nitrates, strontium and barium.
Mercury exposure has been associated with neurological and developmental damage in humans. Arsenic is poison and classified as a human carcinogen. Selenium is a human and environmental toxin. The levels of these and other contaminants in water are regulated by both USA State and Federal Governments and typically they require removal treatment to meet discharge permit levels.
Sorbents are known contaminant removal agents. Activated carbons and functionalized aluminas are examples of effective sorbents used in industrial wastewater treatment. The mechanism of removal of metals and other contaminants by sorbents is by bonding of the contaminant to the adsorbent surface as water containing the contaminant comes in contact with the adsorbent. Activated carbon often is impregnated with additional chemistry that has a bonding affinity for selected contaminants.
Functionalized alumina is an alumina substrate upon which chemistries with affinities for soluble metals are reacted onto the alumina to generate active adsorption sites. In the removal of metals and other contaminants by a functionalized alumina sorbent, it is generally the reacted sites that complex with the soluble metals in fluids to form bonded metal complexes on the surface of the alumina. For instance, sulfur reacted onto an alumina substrate will form mercuric sulfide on the alumina surface when water containing soluble mercury comes in contact with the sorbent. Mercury is removed from the water and permanently bonded to the adsorbent material.